1. Field of the Invention
The present invention relates to a control system for controlling an electric rotating machine.
There is known a control apparatus configured to reduce noise occurring from a PWM inverter as described, for example, in Japanese Patent No. 5121895. The control apparatus described in this patent reduces the noise of a PWM inverter by changing a carrier frequency randomly to change the on-off pattern of the PWM pulse to thereby spread the switching frequency components of the PWM inverter.
However, when the PWM inverter operates at a high modulation factor where the amplitude of a voltage command is large relative to the system voltage of the PWM inverter, since the amplitude of the voltage command exceeds the carrier amplitude of the voltage command, the frequency that the PWM pulse turns on and off reduces. As a result, the on-off pattern of the PWM pulse becomes almost constant even if the carrier frequency is randomly changed. Hence, it is difficult to sufficiently spread the switching frequency components by randomly changing the carrier frequency when the PWM inverter operates at a high modulation factor.